1. Field of the Invention
The present invention relates to novel polysilazanes comprising ##STR2## recurring structural units, hereinafter designated polyhydrosilazanes, and to a process for the preparation of such novel polyhydrosilazanes.
2. Description of the Prior Art
It is known to this art (French Patent 2,190,764) to prepare polysilazanes by reacting a halosilane with a compound bearing one or more NH.sub.2 or NH groups.
Although this '764 patent refers only to the use of amine and, more precisely, of methylamine, a great number of compounds containing an NH.sub.2 or NH group are proposed, among which the hydrazines are included. In this particular case of hydrazine, with CH.sub.3 HSiCl.sub.2 it is found that the reaction is therefore of the type: EQU CH.sub.3 HSiCl.sub.2 +4NH.sub.2 NH.sub.2 .fwdarw.CH.sub.3 SiH(NH--NH.sub.2).sub.2 +2NH.sub.2 NH.sub.2 --HCl
Stated differently the formation of the hydrazinosilazane or cyclosilazane (CH.sub.3 HSiNH--NH).sub.n is accompanied by the formation of a number of moles of hydrazine hydrochloride which is substantially equal to the number of moles of hydrazine bonded onto the silicon atom by the substitution of chlorine. In light of the cost of hydrazine, it then appears necessary to separate off the hydrazine hydrochloride and to recover the hydrazine itself, generally by addition of sodium hydroxide, followed by an azeotropic distillation or a zone crystallization.